Jennifer & Marc Debut Their Labor of Love

At the Toronto Film Festival premiere of Jennifer Lopez and Marc Anthony's movie El Cantante Tuesday, Anthony explained why he and his wife work so well together both onscreen and off: "Just simple love," he said.

Lopez proved it when she walked across the stage and kissed her husband on the lips before introducing the biopic of salsa legend Hector Lavoe, which she and Anthony star in and coproduced.

Did their relationship make it hard to work together? "Marc and I met working, so it wasn't really an issue," she said. "We know each other's work rhythm." Another key to their success: "We don't do anything that we don't believe in. … It was a passion project for both of us, and I've been trying to get it made for five years."

Anthony and Lopez play Lavoe and his wife, Puchi, who had a volatile relationship – but those who worked on the film during its shoot last summer agree that the couple were a great team in real life.

Costar John Ortiz said that on set, "They were holding hands, looking at each other with those eyes that people who are in love look at each other with. I think they are just very huggy-dovey. They're very nurturing."

Said producer Julio Caro, "They're very close. It's a tight relationship. You can tell there's a lot of love there and a lot of respect. Working with them was special."

Anthony and Lopez handled playing a dysfunctional couple well, writer-director Leon Ichaso told PEOPLE. The atmosphere on the set was "Fun, fun. Even when he punched her so hard, he broke through her skin. Marc had to wear so many rings, and one of those blows broke her skin. And we all had a good laugh. She's tough."

Lopez has said she'd like to work on another production with Anthony: a baby. "They have everything else but that," Ichaso said. "That's what would make them good parents. They now have the success and everything else, and they would take the time off to enjoy it. It would complete them."